The present invention concerns pharmaceutical compositions for promoting the healing of wounds or fibrotic disorders, in particular for promoting the healing of wounds or fibrotic disorders with reduced scarring.
By xe2x80x9cwounds or fibrotic disordersxe2x80x9d is meant any condition which may result in the formation of scar tissue. In particular, this includes the healing of skin wounds, the repair of tendon damage, the healing of crush injuries, the healing of eye wounds, including wounds to the cornea, the healing of central nervous system (CNS) injuries, conditions which result in the formation of scar tissue in the CNS, scar tissue formation resulting from strokes, and tissue adhesion, for example, as a result of injury or surgery (this may apply to e.g. tendon healing and abdominal strictures and adhesions). Examples of fibrotic disorders include pulmonary fibrosis, glomerulonephritis, cirrhosis of the liver, and proliferative vitreoretinopathy.
By xe2x80x9creduced scarringxe2x80x9d is meant reduced level of scarring relative to an untreated wound or fibrotic disorder.
In particular, there is a lack of compositions for promoting the healing of wounds or fibrotic disorders with reduced scarring. Scar tissue formation, although providing mechanical strength to a healed wound, can be unsightly and may impair the function of the tissue.
This is particularly the case in wounds which result in scar tissue formation in the CNS, the scar tissue inhibiting the reconnection of severed or re-growing nerve ends, so significantly affecting their function.
Compositions for promoting the healing of wounds or fibrotic disorders may also be used together with compositions for use in the treatment of chronic wounds, for example venous ulcers, diabetic ulcers and bed sores (decubitus ulcers), especially in the elderly and wheel chair bound patients. Such compositions may be extremely useful in patients where wound healing is either slow or in whom the wound healing process has not yet started. Such compositions may be used to xe2x80x9ckick-startxe2x80x9d wound healing and may then be used in combination with the compositions of the present invention. Hence not only may a chronic wound be healed, but it may be healed with reduced scarring.
The activation of LTGF-xcex2 (Latent Transforming Growth Factor-xcex2) to active TGF-xcex2 is a critical step in the healing process. LTGF-xcex2 (which comprises TGF-xcex2 bound to the LAP (Latency Associated Peptide) which in turn may be bound to the LTBP (LTGF-xcex2 Binding Protein)) binds to cell-surface M6P (mannose-6-phosphate) receptors via M6P-containing carbohydrates in the LAP (Purchio, M. F. et al., 1988, J. Biol. Chem., 263: 14211-14215; Dennis, P. A. and Rifkin, D. B., 1991, Proc. Natl. Acad. Sci. USA, 88: 580-584; Shah M. et al., 1992, Lancet, 339: 213-214; Shah, M. et al., 1994, J. Cell Sci., 107: 1137-1157). This binding allows the activation of the LTGF-xcex2 a process also involving transglutaminase and plasminogen/plasmin.
Due to the binding of LTGF-xcex2 to the M6P receptor, M6P itself may play a significant role in the healing process by competing with the M6P-containing carbohydrates in the LAP for the M6P receptor binding site. By increasing the quantity of M6P at a site (by xe2x80x9csitexe2x80x9d in this context is meant a site of wounding or a fibrotic disorder), the binding of LTGF-xcex2 to the M6P receptor may be inhibited (or at least reduced), and the levels of fibrotic and non-fibrotic TGF-xcex2 affected.
Although M6P is extremely useful, it is quickly metabolised and so previous attempts to increase the levels of M6P at a wound site have focused upon providing a constant supply of M6P to the wound site by the use of slow/sustained/biocompatible non-inflammatory delivery systems. Such slow/sustained delivery systems are both costly and inconvenient and are extremely difficult to produce since it is difficult to achieve slow release from a non-inflammatory/biocompatible vehicle.
The present inventor has found that, surprisingly, analogues of M6P may be used to promote the healing of wounds or fibrotic disorders with reduced scarring, the analogues having similar yet distinct structures and functioning as M6P and/or inhibiting the degradation of M6P.
According to the present invention there is provided an analogue of M6P for use in promoting the healing of wounds or fibrotic disorders with reduced scarring.
The analogue may be a phosphonate analogue of M6P or a salt thereof. Such an analogue may, for example, be any one of the molecules of FIGS. 1(a)-(f) or a salt thereof. Surprisingly, it has been found that phosphonate analogues of M6P are capable of binding to the M6P isomerase binding site. This allows them to competitively inhibit the binding of M6P to the binding site and competitively inhibit M6P breakdown (i.e. M6P metabolism), therefore increasing the half-life of M6P. Even more surprisingly, these phosphonate analogues of M6P, despite their molecular similarity to M6P and despite their ability to bind to the M6P isomerase binding site, have significantly greater half-lives than M6P (i.e. are broken down at a significantly slower rate than M6P).
The analogue may have a significantly greater half-life than M6P. The analogue may have a half-life at least approximately 10 times that of M6P. It may, for example, have a half-life at least approximately 100 or 1000 times greater than M6P. It may be metabolised by M6P isomerase at a significantly slower rate than M6P. The analogue may bind the M6P isomerase receptor binding site. It may bind to the cell-surface M6P receptor binding site.
The analogue may bind to the M6P isomerase receptor binding site. It may bind to the cell-surface M6P receptor binding site.
The analogue having a greater binding affinity than M6P for a M6P receptor. The analogue may have a greater affinity than M6P for the M6P isomerase receptor binding site. The analogue may have a binding affinity for the M6P receptor approximately 2 or 3 times that of M6P.
The analogue may be the phosphonate analogue of M6P of FIG. 1(b) or a salt thereof, having a half-life approximately 1000 times that of M6P.
The analogue may be the phosphonate analogue of M6P of FIG. 1(b) or a salt thereof, having a half-life approximately 1000 times that of M6P and a binding affinity for the M6P isomerase receptor binding site approximately 3 times that of M6P.
The analogue may increase the half-life of M6P in an environment containing M6P isomerase. The analogue may be for use in increasing the half-life of M6P in an environment containing M6P isomerase.
The analogue may be for use in the environment of the human or animal body.
The analogue may be for use to promote the healing of wounds or fibrotic disorders with reduced scarring.
The analogue may be an inhibitor of M6P breakdown. It may be an inhibitor of M6P metabolism. It may be an inhibitor of M6P isomerase.
The analogue may be used in conjunction with a composition for promoting the healing of wounds or fibrotic disorders with reduced scarring. Such a composition may comprise M6P. For example, an analogue according to the present invention may comprise a phosphonate analogue of M6P in conjunction with M6P itself.
The analogue may be for use in conjunction with a composition for promoting the healing of chronic wounds.
The analogue may be for use in conjunction with a pharmaceutically acceptable carrier, diluent or excipient.
This means that a single dose of a phosphonate analogue may have a long-lasting effect upon a wound site, providing significant clinical and therapeutic advantages. This in turn means that instead of the present continual supply of M6P to a wound site, a site may be given a single dose, or several doses, of a phosphonate analogue of M6P.
By reducing the dosage of M6P to a wound site, the osmotic effect upon the surrounding tissue at the site may be significantly reduced when compared to the osmotic effect of a continual supply of M6P.
The analogue may be used in conjunction with a pharmaceutically acceptable carrier, diluent or excipient.
Hence the analogue may be functionally equivalent to M6P, yet may have a significantly greater half-life and/or receptor binding affinity than M6P. The analogue may not only function as M6P, but may also act to increase the half-life and efficacy of any added or endogenous M6P by inhibiting the metabolism of M6P by, for example, M6P isomerase.
Also provided according to the present invention is a method for promoting the healing of wounds or fibrotic disorders with reduced scarring comprising the use of an analogue of M6P according to any one of the preceding claims.
The method may comprise administering an analogue of M6P to a site of wounding or fibrosis.
The method may comprise the use of an analogue of M6P either immediately before or immediately after wounding/onset. It may comprise the use of an analogue of M6P within approximately 120 hours of wounding/onset, although it may be preferable to apply it within a shorter time, for example 120, 96, 72, 48, 24 or 12 hours post-wounding/onset By xe2x80x9consetxe2x80x9d is meant the onset of a fibrotic disorder.
The efficacy of the treatment in promoting healing with reduced scarring may be significantly enhanced by increasing M6P levels at a site immediately following wounding when TGF-xcex21 complexed to LAP is released from degranulating platelets. The TGF-xcex21 complexed to LAP is either free in the tissue fluid, bound to the fibrin clot/platelet complex, or is endocytosed into surrounding cells. e.g. fibroblasts, monocytes and macrophages, by the M6P receptor. This degranulation and release of fibrotic TGF-xcex21 upon initial wounding has a number of effects which affect subsequent healing. In particular, the TGF-xcex21 attracts monocytes and macrophages to the site, which in turn release more TGF-xcex21. By inhibiting this initial activation of TGF-xcex21, which is predominantly TGF-xcex21, the ratio of fibrotic:non-fibrotic growth factors at a site may be altered in favour of non-fibrotic growth factors and enhanced healing with reduced scarring effected.
The method may be used in conjunction with a method for promoting the healing of wounds or fibrotic disorders with reduced scarring.
The method may be used in conjunction with a method for promoting the healing of chronic wounds.
Experimental work undertaken in treating wounds with non-phosphorylated mannose and glucose resulted in retarded healing when compared with controls. Galactose-6-phosphate and glycerol-3-phosphate have no effect upon either wound healing or scarring.
The invention will be further apparent from the following example, which shows by way of example only, one form of analogue of M6P which is metabolised at a significantly slower rate and has a greater M6P receptor binding affinity than M6P and may be used to inhibit M6P metabolism.